The present invention relates to organic electroluminescent display devices with preformed images.
Photographic images are commonly printed on paper, fabric, ceramics and other substrate media that provide a reflective or transmissive substrate for the handling and viewing of said images. These substrates often include a reflective surface as background that allows direct viewing of the images using ambient light or other forms of applied illumination. Transparency photographic media such as slides or transparency display media require a lit backing or projecting system that illuminates said transparency media to either view directly (displays) or project onto screens (slides). The choice for the type of photographic medium depends on the specific application, e.g. consumer images for home display, commercial billboards, lit advertising displays, or many others.
For either type of application, current media suffer a number of drawbacks. Reflective photographic media require ambient illumination for viewing; a darkened living room, for example, may not provide sufficient illumination levels for enjoyable viewing. Transparency media, on the other hand, require the expense and additional bulk of light sources, view boxes, and associated subsystems. For projection displays, supplemental screens, darkened rooms, and optical projection systems are normally required.
Flat panel display technology has provided in some cases solutions to the illumination and bulk problem. Devices such as Liquid Crystal Displays (LCDs) are electronically-controlled transparencies that when back illuminated with thin profile light sources provide an integrated and reasonably compact system to view pictorial and graphical content. Unfortunately, LCD""s have problems with brightness, angle of viewing and, although superior to the illuminated view box, are still bulky relative to a standard print on paper.
Organic Electroluminescent Display Devices (OEL""s) are flat panel display media that do not require external illumination sources and hence are advantaged in compactness and power consumption. OEL""s are also Lambertian emitters and do not exhibit significant angle viewing problems. Eastman Kodak U.S. Pat. Nos. 4,356,429 and 4,539,507 describe some OEL""s device configurations and materials. In order to depict pictorial and other types of content on LCD""s, OEL""s, and other flat panel display devices, x-y addressable electronic subsystems are required to apply controlled voltages across the display medium that are representative of the image being displayed. Voltage applied across OEL""s, for example, controls the amount of current that flows through a light emitting layer that produces light of color and brightness controlled by the chemical and physical characteristics of said layer. A multiplicity of colors can be achieved using OEL technology by chemical manipulation of the layers as taught in U.S. Pat. No. 4,769,292.
The specific voltage applied at an x-y location in flat panel display media can be controlled using a number of approaches. In the so-called passive matrix device, orthogonal sets of electrodes are sequentially addressed in a line-by-line manner with voltage levels that correspond to the image brightness desired at each specific x-y location of the display device. In the active matrix configuration, a set of addressable transistors is commonly defined on single crystal silicon or Si-on-glass (thin film transistors). The transistors are switched to supply voltages across the active area display medium. U.S. Pat. No. 5,684,365 describes an active matrix display that uses organic electroluminescent materials for the display medium.
There are many applications where it is desired to display single or preformed emissive images using a low cost display device. Some applications include point of purchase displays, signs, and even traditional consumer photography. Although flat panel displays are more flexible in their ability to display arbitrary and changeable content that their traditional printed or photographic counterparts, their cost is still relatively high due to device complexity, the electronic interconnections, and the driving circuitry required. Flat panel displays become extremely expensive at the larger sizes due to the semiconductor processes used to fabricate them and the fact that cost scales with display area. The need for high resolution increases the multiplicity and complexity of the drive electronics, resulting in further additional cost.
It would therefore be desirable to have a low cost, large area emissive device capable of displaying high quality preformed images. Ideally, such a display would be produced using low cost printing technology similar to photographic, thermal transfer, offset printing, ink jet to name a few. In fact, it would be desirable if such a display xe2x80x9cdevicexe2x80x9d would have the availability and price point closer to a xe2x80x9cconsumablexe2x80x9d such as a photographs, transparencies, or printed material.
U.S. Pat. No. 5,041,326 to Schroder et al. discloses an electroluminescent laminate assembly that may be used to display preformed emissive images. The luminescent laminate assembly is defined using a layer having light emitting particles, said layer interposed between a pair of electrically conducting matter electrodes, at least one of them being transmissive to the emitted light. Different gradations of light intensity are achieved by spatially controlling the thickness of the light emitting layer and of the electrically conducting matter. Further, the color or hue of the image may be controlled by modifying the thickness and color of the light emitting particles in accordance to the color or hue desired. The defined patterns are produced using masking, doctor-blading, embossing, and/or spraying processes. Although this assembly is capable of forming preformed images, it is best suited to display simple drawings, graphics, and patterns. Furthermore, since in accordance to their claims, the thickness or concentration of at least one of the electrode layers must be varied to modulate light output, the brightness and color spectrum of the image cannot be controlled independently to achieve their full brightness and spectral ranges. Finally, Schroder et al. do not specifically teach a way to achieve a high quality continuous tone images using their invention.
It is therefore an object of the present invention to provide a display device with preformed images that offers the advantages in compactness and ease of viewing of emissive flat panel displays having preformed continuous tone images
It is a further object of the present invention to make use of the advantages of organic electroluminescent display devices to form preformed images.
Another object of the invention is to provide large scaleable flat panel emissive display devices that have preformed images and can be easily mounted onto standard photographic picture frames, not much thicker than the glass cover of traditional picture frames.
It is a further object of this invention to provide consumers a conveniently method to obtain light emissive images from pictures using photographs of their choice and standard photographic fulfillment channels.
These objects are achieved by an organic electroluminescent display device that displays a preformed image, comprising:
a) spaced anode and cathode electrodes;
b) organic electrically conductive hole transport layer and electron transport layer disposed between the anode and cathode electrodes;
c) a preformed image layer formed between the organic electrically conductive hole transport layer and electron transport layers such layer having a region that is preformed to have at least one characteristic such that when a voltage is applied across the anode and cathode electrodes which will cause a preformed image to be displayed; and
d) means for applying a voltage to the anode and cathode electrodes to cause the emission of light to display the preformed image.
It is an advantage of the present invention that by having a layer with a preformed image and using such layer in an organic electroluminescent display device, high resolution full color preformed images can be effectively displayed.
The present invention does not require electronic addressing systems, complex electronic support components and interconnects, or bulky and expensive light emitting or projection systems.
Another advantage of the present invention is that the display devices in accordance with the present invention can be made so as to have the cost and usability akin of a consumable media.
Another advantage of the present invention is that the display devices in accordance with the present invention are able to display high quality continuous tone color images that exhibit fully controlled color gamut and brightness.